892 CHAPTER 21: Electrochemistry
Key Terms
Alkaline cell A dry cell in which the electrolyte contains KOH.
Ampere Unit of electric current; 1 ampere equals 1 coulomb per
second.
Anode The electrode at which oxidation occurs.
Cathode The electrode at which reduction occurs.
Cathode protection Protection of a metal against corrosion by
making it a cathode (attaching it to a sacrificial anode of a more
easily oxidized metal).
Cell potential Potential difference, Ecell, between reduction and
oxidation half-cells; may be at nonstandardconditions.
Concentration cell A voltaic cell in which the two half-cells are
composed of the same species but contain different ion con-
centrations.
Corrosion Oxidation of metals in the presence of air and
moisture.
Coulomb Unit of electric charge; the amount of charge that
passes a given point when 1 ampere of electric current flows
for 1 second.
Downs cell An electrolytic cell for the commercial electrolysis
of molten sodium chloride.
Dry cells Ordinary batteries (voltaic cells) for flashlights, radios,
and so on; many are Leclanché cells.
Electrochemistry The study of the chemical changes produced
by electric current and the production of electricity by chemi-
cal reactions.
Electrode potentials Potentials, E,of half-reactions as reduc-
tions versus the standard hydrogen electrode.
Electrodes Surfaces on which oxidation and reduction half-
reactions occur in electrochemical cells.
Electrolysis The process that occurs in electrolytic cells.
Electrolytic cell An electrochemical cell in which electrical
energy causes nonspontaneous redox reactions to occur.
Electrolytic conduction See Ionic conduction.
Electroplating Plating a metal onto a (cathodic) surface by
electrolysis.
Faraday An amount of charge equal to 96,485 coulombs; corre-
sponds to the charge on one mole of electrons, 6.022 1023
electrons.
Faraday’s Law of Electrolysis The amount of substance that
undergoes oxidation or reduction at each electrode during elec-
trolysis is directly proportional to the amount of electricity that
passes through the cell.
Fuel cell A voltaic cell in which the reactants (usually gases)
are supplied continuously and products are removed continu-
ously.
Galvanic cell See Voltaic cell.
Half-cell The compartment in a voltaic cell in which the oxida-
tion or reduction half-reaction occurs.
Hydrogen–oxygen fuel cell A fuel cell in which hydrogen is
the fuel (reducing agent) and oxygen is the oxidizing agent.
Ionic conduction Conduction of electric current by ions through
a pure liquid or a solution.
Lead storage battery A secondary voltaic cell that is used in
most automobiles.
Leclanché cell A common type of dry cell.
Metallic conduction Conduction of electric current through a
metal or along a metallic surface.
Nernst equation An equation that corrects standard electrode
potentials for nonstandard conditions.
Nickel–cadmium cell (nicad battery) A dry cell in which the
anode is Cd, the cathode is NiO 2 , and the electrolyte is
basic.
Polarization of an electrode Buildup of a product of oxidation
or reduction at an electrode, preventing further reaction.
Primary voltaic cell A voltaic cell that cannot be recharged; no
further chemical reaction is possible once the reactants are
consumed.
Sacrificial anode A more active metal that is attached to a less
active metal to protect the less active metal cathode against
corrosion.
Salt bridge A U-shaped tube containing an electrolyte that con-
nects two half-cells of a voltaic cell.
Secondary voltaic cell A voltaic cell that can be recharged; the
original reactants can be regenerated by reversing the direction
of current flow.
Standard cell A cell in which all reactants and products are in
their thermodynamic standard states (1 Mfor solution species
and 1 atm partial pressure for gases).
Standard cell potential The potential difference, E^0 cell, between
standard reduction and oxidation half-cells.
Standard electrochemical conditions 1 Mconcentration for
solution species, 1 atm partial pressure for gases, and pure solids
and liquids.
Standard electrode A half-cell in which the oxidized and
reduced forms of a species are present at unit activity: 1 Msolu-
tions of dissolved species, 1 atm partial pressure of gases, and
pure solids and liquids.
Standard electrode potential By convention, the potential
(E^0 ) of a half-reaction as a reduction relative to the standard
hydrogen electrode, when all species are present at unit
activity.
Standard hydrogen electrode (SHE) An electrode consisting
of a platinum electrode that is immersed in a 1 MHsolution
and that has H 2 gas bubbled over it at 1 atm pressure; defined
as the reference electrode, with a potential of exactly0.0000...
volt.
Voltage Potential difference between two electrodes; a measure
of the chemical potential for a redox reaction to occur.
Voltaic cell An electrochemical cell in which spontaneous chem-
ical reactions produce electricity; also called a galvanic cell.